<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
    var num = parseInt(prompt("请输入一个整数"));
    var sum = 0;
    for(var i = 3; i <= num; i++){
       sum += i / (i-1);
    }
    alert(sum);
</script>
</html>